1. Field of the Invention
The present invention relates generally to a method of modulation and demodulation of a data signal and an apparatus for carrying the same out, and is directed more particularly to a method of data modulation and an apparatus for carrying the same suitable for use in magnetically recording (or reproducing) data, in which pulse-code-modulating (PCM) is utilized, for example, for audio signal, in recording the digitized sound signals on a disc and reproducing the recorded signals on the disc.
2. Description of the Prior Art
In conventional magnetic recording and reproducing, in order to record data at high density and reproduce the data without error, it is desired that the minimum distance of magnetic inversions is long and that the maximum distance therebetween is short. Also, it is important that the width of a window used for detecting the data be selected wide. To achieve this end, a modulation system has been proposed earlier in which a data word of three bits is converted into a code word of six bits and, in the finally provided code word of six bits, at least two "0"'s or spaces occur between successive "1"'s or marks. This modulation system is commonly known as 3PM (three position modulation).
In fact, the bit number, or word length of data words of a PCM signal, such as that provided by pulse-code-modulating an audio signal, and is commonly selected to be 2.sup.n, for the reason that a digital circuit for processing data is usually formed of conventional circuit elements so as to achieve a simple circuit construction. For example, when PCM data of 16 bits are modulated by 3PM, since the bitnumber such PCM of data is not a multiple of three, the data words can not be processed by conventional digital division at their inherent word boundaries.